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Baseline FDG PET/CT-Defined Axillary Burden Predicts Axillary Pathologic Complete Response After Neoadjuvant Therapy
Mehmet Tarık Tatoğlu1, İlker Nihat Ökten2, Ebru Ibisoglu3
1TC Saglik Bakanligi Goztepe Prof Dr Suleyman Yalcin Sehir Hastanesi, Nuclear Medicine, Türkiye, Istanbul.
Aim:
Predicting axillary pathologic complete response (pCR) after neoadjuvant systemic therapy (NST) may enable risk-adapted axillary management in clinically node-positive breast cancer (BC), but practical baseline PET-derived predictors are limited.
Methods:
Single-center retrospective cohort of consecutive cN+, M0 patients with baseline [18F]FDG PET/CT-reported axillary nodal metastasis treated with NST and surgery (complete-case n=115). Axillary pCR was defined as no residual invasive carcinoma in axillary lymph nodes; isolated tumor cells and/or micrometastases were classified as non-pCR. Two prespecified ridge-penalized logistic models combined routine clinical variables with baseline PET-defined axillary burden as (i) hypermetabolic ALN count (Model A) or (ii) limited (1-3) versus advanced (≥4) burden group (Model B). Stratified 5-fold cross-validation generated out-of-fold (OOF) predictions; AUC, Brier score, and logistic recalibration slope/intercept were bootstrapped on OOF predictions (2000 resamples).
Results:
Axillary pCR occurred in 59/115 (51.3%). Discrimination was good: AUC 0.80 (95% CI 0.72-0.88) for Model A and 0.79 (95% CI 0.71-0.87) for Model B. Calibration was acceptable (bootstrap-mean slope/intercept ≈1.10/0.04 and 1.08/0.03, respectively). Greater baseline PET-defined axillary extent was associated with lower odds of pCR; molecular subtype and neoadjuvant anti-HER2 therapy remained strongly associated with response.
Conclusion:
Prespecified ridge models combining routine clinical variables with baseline [18F]FDG PET/CT-defined axillary burden showed good internal performance for predicting axillary pCR. External validation is required before response-adapted clinical use.
